Several processes for producing low-lactose and lactose-free milk by using membrane techniques are known. A conventional enzymatic process for splitting lactose is also generally known in the field, the process comprising the step of adding lactase from fungus or yeast to milk in such a manner that lactose is split into monosaccharides, i.e. glucose and galactose, in over 80%.
Several membrane filtration process solutions have been presented for removing lactose from milk raw material. Four basic membrane filtration processes are generally used: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). Of these, UF is mainly suitable for separating lactose from milk. Reverse osmosis is generally applied to concentration, ultra- and microfiltration to fractionation, and nanofiltration to both concentration and fractionation. A lactose removal process based on a membrane technique is described in WO publication 00/45643, for instance, wherein lactose is removed by ultrafiltration and diafiltration. When filtration processes are used, the problem often created is the generation of side fractions, such as a permeate or lactose fractions. Published US application 2007/0166447 discloses the use of a lactose-containing NF retentate fraction generated as a side fraction as the raw material of fermentation in the production of yoghurt, for example.
Recent studies have indeed been concentrated on the membrane filtration of milk and to the use of such filtrated, low-carbohydrate milk in the production of dairy products, such as cheese, ice cream and yoghurt. It is common to the known, multi-step membrane filtration processes comprising several different processes that the processes include the separate addition of water, which does not originate from the milk raw material, for diluting milk components and for obtaining a suitable sweetness in milk products containing little carbohydrate (i.a. lactose). It is particularly problematic in the field that a product containing liquid that does not completely originate from the original milk raw material cannot be called milk. It is also common to known processes that the residual lactose is not removed until from the membrane-filtrated milk raw material.
It is known in the field that a problem with membrane techniques in general is that during ultrafiltration not only lactose is removed from the milk, but also some of the minerals that are significant to the taste of milk and milk products prepared thereof. Controlling the mineral content is particularly problematic in the field, and extensive loss results from the known processes, which is why these minerals must often be returned or added separately.
Often membrane processes also produce, for instance, sugar-containing and mineral-containing secondary flows, which cannot be exploited efficiently and which also increase waste water load, require further processing and add to the costs.
WO publication 2005/074693 discloses the use of the membrane technology in the production of lactose-free milk. It is typical of the process that the ultrafiltration retentate is diluted with water, resulting in a lactose content of about 3.0%. The residual lactose is hydrolyzed enzymatically.
WO publication 03/094623 A1 discloses a process in which a milk product is ultrafiltered, nanofiltered, and concentrated by reverse osmosis, after which the minerals removed during ultrafiltration are returned to the UF retentate. The residual lactose of the thus obtained low-lactose milk product is hydrolyzed with a lactase enzyme into monosaccharides, whereby an essentially lactose-free milk product is obtained. With this process, lactose is removed from milk without affecting the organoleptic properties of the milk product being prepared. In the process for producing a milk product, water not originating from any steps of said process is added. Also, the process produces minerals containing secondary flows, which cannot be utilized in the process and which require post-processing.
Patent publication KR20040103818 describes a process for the production of low-lactose milk, comprising nanofiltering milk hydrolyzed with lactase to partially remove galactose and glucose, and adding water to the nanofiltration retentate to achieve a suitable sweetness. Choi et al. (Asian-Aust. J. Anim. Sci 20 (6) (2007) 989-993) describe a process for the production of lactose-hydrolyzed milk, wherein raw milk is hydrolyzed with β-galactosidase (5 000 lactase activity unit/g, Validase, Valley Research) partially (0.03%; 4° C., 24 hours) or ‘completely’ (0.1%; 40 h), heat-treated to inactivate the enzyme (72° C., 5 min), cooled to 45 to 50° C., and nanofiltered at a pressure of approximately 9 to 10 bars (130 to 140 psi; concentration factor 1.6). Water was added to the NF retentate and the heat treatment was performed at 65° C. for 30 min. The processes disclosed in said publications and comprising a hydrolysis step, heat treatment of the enzyme, nanofiltration, and addition of water, are not suitable as such for the production of a milk product without separate addition of water. The process also comprises separate heat treatment for inactivating the enzyme and for eliminating microbiological problems in the filtration step (i.e. in NF filtration in a warm environment). The high hygiene requirements of milk processing also set limitations on industrial processes. In the industrial processing of milk raw material and membrane processes, a temperature of e.g. 10° C. is generally desirable for eliminating microbiological problems.
It is therefore desirable to provide processes for controlling also the secondary flows in the process and for recovering them more efficiently than at present, which also enables new kinds of applications. Thus, the processes are made still more effective. However, it is extremely challenging to achieve products having a completely flawless taste and structure and meeting consumers' expectations of an organoleptically acceptable milk product and being produced economically and simply without separate addition of water.
A process for the production of low-lactose and lactose-free milk products that are completely flawless in their organoleptic properties without any extra costs has now been unexpectedly invented. The process of the invention enables a more efficient and simpler control of milk components as compared with conventional processes without special additional costs and with minimized losses. No separate addition of water is required in the production of a milk product. In addition, the process of the invention does not generate secondary flows requiring post-processing, making the process more efficient.